The use of optical frequencies for the transmission of telecommunications signals has resulted in the development of many active components which operate at optical frequencies. Examples of such active components include, optical sources, optical detectors, modulators and switches. Although these components operate on optical signals, they are usually controlled electronically. Thus a device which contains one or more of the active elements must also provide paths for the optical (traffic) signals and paths of the electrical control signals.
Thus the complete device performs electronic and optical functions and it is usual to employ the term "optoelectronic devices".
It is particularly desirable to implement optoelectronic devices in integrated forms wherein the paths and the active elements are produced as layers, e.g. by epitaxial deposition and etching. In such structures the optical paths take the form of suitably configured strips of transmissive material, e.g. indium phosphide and gallium arsenide. It is, of course, necessary to couple the paths to the active devices and it has been established that tapered configurations are particularly effective for coupling an optical path to an active device. It will be appreciated that the tapers need to be accurately located and dimensioned. It is an object of this invention to facilitate the production of such tapers.
It is well established to produce optical paths by irradiation controlled electrolytic etching. A paper by Bell Laboratories describes the production of lenses by such techniques and it states that arbitrary features can be produced by appropriate light patterns. U.S. Pat. No. 4,415,414 describes the use of masks consisting of alternate opaque and clear rings to produce lenses.